A Novel Multi Unit Bioreactor (MUB) Used for Solid State Fermentation.

Mythreyi Chandoor, Deepak Singh, Gadekar Sachinand Shulin Chen

The process Description:

The biomass (wheat straw) has to be pretreated in order to extract sugars which are finally utilized for ethanol production. Biological pretreatment requires the biomass to be used as a substrate for the microorganism.The name of the bioreactor in this study will be Multi Unit Bioreactor. The following are the main steps of the process considered while designing the bioreactor:

  1. Spore cultivation
  2. Biomass loading
  3. Biomass sterilization
  4. Spore inoculation on biomass
  5. Aeration
  6. Incubation temperature at 37oC
  7. Maintaining moisture level
  8. Unloading of pretreated biomass
  9. Cleaning of the bioreactor.

Novel technologies in this process:

1. Spore cultivation technique

2. Solid State fermentation of the Biomass for the Pretreatment.

Process description

1. Spore cultivation:

Preparation of fungal cultures for the biomass degradation is an important step in the biological based biorefinery system. It includes the cultivation of microbe in a medium in a large scale and producing spores to make effective inoculums. Generally, fungal spores are prepared by using potato dextrose agar (PDA) and preparing spores in a bulk amount is not cost effective by using this commercial medium. In this study, we have chosen food waste based medium as a cheapest medium for the cultivation of the spores. The fresh spores were obtained within seven days of incubation at 30 oC.

Small scale experiment in the lab:

Materials and methods:

Food waste with total solid content (23%) was obtained from a restaurant in Pullman, WA. These wastes were ground to paste and made the suspension of different concentration (1 to 100%). Agar was added to the liquid to make the surface smooth. The media were autoclaved and inoculated with spores. Spores were harvested after seven days incubation at 30 oC.

2. The mechanical construction of spore tank:

The spores are grown in a tank which consists of food waste mixed with agar in the required proportions as mentioned above. These are cultured in a huge tank. The spores are grown on the surface of the food waste. Once for every seven days the spores are collected. During the process of collection first water is poured over the surface of the tank. As the food waste is mixed with agar, is stagnant and solid. Swapping of the spores from the surface from the tank will be called scarping. This is done with a help of a comb like device attached to one end of the container and it rotates covering the complete surface and this flows into the spore collection tank. The addition of water to the spores is in the ratio of (500ml of spores/ Liter of total medium).

The spore cultivation tank will be designed as a sterilization unit. Here, the medium can be reused more than 4 times.

Water is required for scrapping

3. Process description:

The process is divided into different steps they are:

  1. Loading the Bioreactor with Biomass-
  2. Immersing it into water
  3. Inoculation of spores
  4. Control the Moisture , Temperature of the Bioreactor
  5. Unloading of the Biomass from the Bioreactor.

The parameters which are required to check in this process are mainly the homogenized distribution of the air and temperature maintenance in the biomass which is required for the growth of Spores. Thetemperature has to be maintained at 37 degrees centigrade. Because the wheat straw has pectin and other components, the microbial contamination is not a serious problem. And the fungal strain used for pretreatment is not harmful to human as it is an aerobic microorganism. So the level of sterilization of the biomass before the spore inoculation with hot air at 110 degrees centigrade is enough for the biomass sterilization. As the parameters considered are temperature control and moisture content. The temperature control is done by Thermister. (Temp range of -60 -160 degree)Thermally sensitive resistors (thermistors) are used widely in detector cooling applications because of their high sensitivity, small size, ruggedness, fast response times, and low cost.{ Is this feasible ???? )

Working of a thermistor

4. MUBdesign:

A single stage layer - Shutter system.

5. How does MUB work?

  1. Loading the Bioreactor with Biomass-

The wheat straw would be filled with a help of conveyer belt which will transport the biomass from the storage unit to the pretreatment station .As the each shutter opens from the single storage storing unit the biomass would be respectively filled in each unit .After the complete loading of biomass in the complete floor it will be immersed in hot water for (???)minutes and lifted up.

The loading of biomass would be complete once the lowest floor is filled with wheat straw.

  1. Inoculation of spores :

The spore cultivation and dilution to make it a spore spray would be dealt under a separate section. Spore inoculation over the wheat straw would be done after the loading of biomass is complete. The spore inoculums are made with a dilution of (????). The inoculums are sprayed with the help of inserted sprinklers which are present at different depths in each single unit.

  1. Control the Moisture , Temperature of the Bioreactor :

The temperature and moisture is controlled with the help a temperature controller (Thermister), and by passing hot and cold air respectively.

  1. Unloading of the Biomass from the Bioreactor: The unloading of biomass would be floor wise .The last one which was loaded would be the first one to be unloaded. Unloading would be done by sliding the bottom of each floor in a way that complete wheat straw is thrown down onto the collector .Each floor is washed with the sprinkles in a way that the complete unloading is done.

All the pretreated wheat straw is collected with the help of collector situated at the bottom of the reactor.

The Bioreactor is made of single processing units which are monitored as a whole system. Thecomplete system is provided with a thermister which would act as a temperature controller.Maintenance of the optimum moisture level in the biomass is done by the water flow into it periodically .The air flow is maintained by using Hepa-Filter at the side wall of the TGB installed roomand the CO2is collected with an exhaust to one end of the room (It can be a point source of CO2). The biomass is sent into the feeder with the help of a biomass loader. The biomass distribution will be controlled by the individual units as described above. As the biomass is very light weight the support required to stand is not high therefore tall structure with many individual units can be constructed, thus, total area unit occupied by the reactor will be small. The steam is sent through a pipe so, the metallic support needed can be made of normal metal used for all kinds of laboratory purpose.

For a pilot scale study for scale up of the bioreactor in a way that it can be used for an output of there needs to be pilot scale study for studying few parameters which includes following work:

Mathematical models required for the following:

  1. Spore Cultivation
  2. Spore dilution and distribution as required
  3. Microbial growth kinetics and its enzyme action on the wheat straw

Matlab to be used for the following:

  1. Spore cultivation
  2. Spore distribution process
  3. MUB working
  • Loading
  • Aeration
  • Unloading

Aspen to be used for:

  1. Cost effective analysis of the equipment
  2. Spore production cost.